1. Field of the Invention
The present invention relates to a process for modifying the surface of flame retardants by encapsulating the particles with a silicon-containing coating agent, and to the corresponding flame retardants themselves and their use.
2. Discussion of the Background
It is known that ammonium phosphates, ammonium polyphosphates, melamine phosphates, melamine borates and melamine cyanurates can be used as halogen-free flame retardants, e.g. for plastics. EP 0 584 567 A1 discloses a flame-retardant plastic molding composition made from olefin polymers and from a flame-retardant system made from ammonium polyphosphate and from a polycondensate made from tris(2-hydroxyethyl) isocyanurate and from an aromatic polycarboxylic acid. DE-A 33 16 880 describes a process for preparing hydrolysis-stable, water-insoluble ammonium polyphosphates by coating with, respectively, melamine-formaldehyde resins and phenol-formaldehyde resins. EP 0 180 790 A1 moreover describes a coated, powder ammonium polyphosphate in which polyurea, i.e. a reaction product made from isocyanate and water, is used for the encapsulation procedure.
Although ammonium polyphosphates, for example, give such plastics good flame retardancy, a disadvantage is that they migrate out of the plastic during the course of its service life and are washed out by environmental agents, such as moisture, since in particular untreated ammonium polyphosphates, but also other phosphoric acid derivatives, have considerable solubility in water.
Cured silicone resins have also been described as a coating material. JP-A 3-131 508, for example, teaches the encapsulation of ammonium polyphosphate as a slurry in an organic solvent with a curable silicone resin, where small amounts of an aminotriethoxysilane are used as a curing agent. However, a joint feature of all of these processes is that the preparation of such surface-treated flame retardants is very complicated, and this noticeably increases the cost of the product. In addition, environmental problems are caused by the use of environmentally unfriendly solvents and by the resultant wastewater and residues.
An object of the present invention is to provide a simple and environmentally friendly process for modifying the properties of flame retardants, such as ammonium polyphosphates.
According to the invention this object has been achieved as described in the claims.
Surprisingly, it has been found that surface-modified flame retardants can be obtained in a simple, cost-effective and at the same environmentally friendly manner by applying an organofunctional-silane or a mixture of organofunctional silanes or an oligomeric organosiloxane or a mixture of oligomeric organosiloxanes or a solvent-containing preparation based on monomeric organosilanes and/or on oligomeric organosiloxanes or a preparation based on water-soluble organopolysiloxanes to a powder flame retardant. The present invention also provides surface-modified flame retardants which are prepared by this process.
As used hereinafter, the phrase xe2x80x9corganic silicon compositionxe2x80x9d means an organofunctional-silane or a mixture of organofunctional silanes, an oligomeric organosiloxane or a mixture of oligomeric organosiloxanes, or a solvent-containing preparation based on monomeric organosilanes and/or on oligomeric organosiloxanes, or a preparation based on water-soluble organopolysiloxanes, or mixtures of any or all of these.
The phrase xe2x80x9csolvent-containing preparation based onxe2x80x9d means that the preparation referred to is prepared by mixing at least the compounds it is based on with a solvent.
A suitable method of applying here is direct dropwise addition, injection or spraying of the coating agent into a fluidized bed of the flame retardant to be treated, whereupon the coating agent generally reacts with the surface of the flame retardant and thus encapsulates the particles. Water of condensation, and also in some cases small amounts of alcohol, can be produced here by condensation or hydrolysis, and these are introduced with the exhausted process air in a manner known per se into an exhaust air purification procedure, e.g. a condensation or catalytic or thermal post-incineration procedure.
A cost-effective and environmentally friendly, and therefore particularly advantageous, method is to use an aqueous preparation based on water-soluble organopolysiloxanes, since virtually exclusively water escapes into the exhausted process air. An additional factor is that explosion protection of the plant is unnecessary. The method of operation described, furthermore, does not produce any filtration residues or wash water.
The present invention provides a process for modifying the surface of flame retardants by encapsulating the particles with a silicon containing coating agent, by applying an organofunctional silane or a mixture of organo functional silanes or an oligomeric organosiloxane or a mixture of oligomeric organosiloxanes or a solvent-containing preparation based on monomeric organosilanes and/or on oligomeric organosiloxanes or a preparation based on water-soluble organopolysiloxanes to a powder flame retardant. The flame retardant is kept in motion during the coating procedure.
The novel process preferably uses from 0.05 to 10% by weight, particularly preferably from 0.1 to 3% by weight, very particularly preferably from 0.5 to 1.5% by weight, of silicon-containing coating agent, based on the amount of flame retardant. The coating agent may be applied over a period of from 10 seconds to 2 hours at a temperature of from 0 to 200xc2x0 C., preferably over a period of from 30 seconds to 10 minutes at a temperature of from 20 to 100xc2x0 C., particularly preferably over a period of from 1 to 3 minutes at a temperature of from 30 to 80xc2x0 C.
The flame retardant encapsulated with coating agent may be post-treated by exposure to heat or to reduced pressure, or to reduced pressure together with heat. This post-treatment of the flame retardant encapsulated with coating agent preferably takes place at a temperature of from 0 to 200xc2x0 C., particularly preferably at a temperature of from 80 to 150xc2x0 C., very particularly preferably at a temperature of from 90 to 120xc2x0 C.
The process may be carried out in a stream of air or of inert gas, such as nitrogen or carbon dioxide. The process may also be carried out by repeating the coating procedure, and if desired a subsequent drying of the encapsulated flame retardant, one or more times.
The flame retardants used in the novel process preferably have an average particle size (d50) of from 1 to 100 xcexcm, particularly preferably from 2 to 25 xcexcm, very particularly preferably from 5 to 15 xcexcm. A suitable method is to use a powder flame retardant of this type in dry, i.e. free-flowing, form.
Flame retardants preferably used in the novel process are:
ammonium orthophosphates, e.g. NH4H2PO4, (NH4)2HPO4 or mixtures of these (e.g. FR CROSS(copyright) 282, FABUTIT(copyright) 747 S), ammonium diphosphates, e.g. NH4H3P2O7, (NH4)2H2P2O7, (NH4)3HP2O7, (NH4)4P2O7 or mixtures of these (e.g. FR CROS(copyright) 134), ammonium polyphosphates, in particular but not exclusively those found in J. Am. Chem. Soc. 91, 62 (1969), e.g. those with crystal structure phase 1 (e.g. FR CROS(copyright) 480), or with crystal structure phase 2 (e.g. FR CROS(copyright) 484) or mixtures of these (e.g. FR CROS(copyright) 485), melamine orthophosphates, e.g. C3H6N6.H3PO4, 2C3H6N6.H3PO4, 3C3H6N6.2H3PO4, C3H6N6.H3PO4, melamine diphosphates, e.g. C3H6N6.H4P2O7, 2C3H6N6.H4P2O7, 3C3H6N6.H4P2O7 or 4C3H6N6.H4P2O7, melamine polyphosphates, melamine borates, e.g. BUDIT(copyright) 313, melamine cyanurate, e.g. BUDIT(copyright) 315, melamine borophosphates, melamine 1,2-phthalates, melamine 1,3-phthalates, melamine 1,4-phthalates and melamine oxalates.
The organofunctional silanes used in the novel process are preferably alkoxysilanes with aminoalkyl or epoxyalkyl or acryloxyalkyl or methacryloxyalkyl or mercaptoalkyl or alkenyl or alkyl functionality, and in a suitable method the abovementioned hydrocarbon moieties contain from 1 to 8 carbon atoms and the alkyl groups may be linear, branched or cyclic. Particularly preferred organofunctional alkoxysilanes are: 3-aminopropyltrialkoxysilanes, 3-aminopropylmethyldialkoxysilanes, 3-glycidyloxypropyltrialkoxysilanes, 3-acryloxypropyltrialkoxysilanes, 3-methacryloxypropyltrialkoxysilanes, 3-mercaptopropyltrialkoxysilanes, 3-mercaptopropylmethyldialkoxysilanes, vinyltrialkoxysilanes, vinyltris(2-methoxyethoxy)silane, propyltrialkoxysilanes, butyltrialkoxysilanes, pentyltrialkoxysilanes, hexyltrialkoxysilanes, heptyltrialkoxysilanes, octyltrialkoxysilanes, propylmethyldialkoxysilanes and butylmethyldialkoxysilanes, and the alkoxy groups are in particular methoxy, ethoxy or propoxy groups.
The oligomeric organosiloxanes which can be used in the novel process are in particular those found in EP 0 518 057 A1 and DE 196 24 032 A1, hereby incorporated by reference. It is preferable in the present process to use those which, as substituents, have (i) alkyl and alkoxy groups, in particular linear, branched or cyclic alkyl groups having from 1 to 24 carbon atoms and alkoxy groups having from 1 to 3 carbon atoms, or (ii) vinyl and alkoxy groups and, if desired, alkyl groups, in particular alkoxy groups having from 1 to 3 carbon atoms and, if desired, linear, branched or cyclic alkyl groups having from 1 to 24 carbon atoms, where the abovementioned oligomeric organoalkoxysiloxanes preferably have a degree of oligomerization of from 2 to 50, particularly preferably from 3 to 20. Particular preference is given here to oligomeric methoxysilanes with vinyl functionality, such as DYNASYLAN(copyright) 6490 or oligomeric methoxysilanes with propyl functionality, for example DYNASYLAN(copyright) BSM 166.
In the process a solvent may be used which contains preparation based on monomeric organoalkoxysilanes and/or on oligomeric organoalkoxysiloxanes, where this preferably comprises methanol, ethanol, n-propanol, isopropanol and/or water as solvent. Such solvent-containing preparations may also comprise emulsifiers. Preparations based on water-soluble organopolysiloxanes, as found in particular in EP 0 716 127 A2, EP 0 716 128 A2, EP 0 675128 A1 and DE 5 196 39 782 A1, all of which are hereby incorporated by reference, may advantageously be used.
Particular preference is given to the use in the novel process of a preparation based on water-soluble organopolysiloxanes, where the organopolysiloxanes contain, besides OH groups, at least one group with aminoalkyl functionality and, if desired, at least one other functional group selected from alkyl, in particular n-alkyl having from 1 to 8 carbon atoms, alkenyl, in particular vinyl, glycidyl ether alkyl, methacryloxyalkyl and mercaptoalkyl, and an organofunctional group is bonded to each silicon atom of the organopolysiloxanes and the average degree of oligomerization of the organopolysiloxanes is from 2 to 50, particularly preferably from 3 to 20.
It is particularly preferable in the novel process to use an aqueous preparation which has a content of less than 0.5% by weight of alcohol, based on the entire preparation, and a pH of from 2 to 6 or from 8 to 12.
It is very particularly preferable here to use a water-based preparation of practically completely hydrolyzed organopolysiloxanes, where the organopolysiloxanes contain in particular 3-aminopropyl groups and vinyl groups as functional groups, and each-silicon atom of the organopolysiloxanes carries an organofunctional group, for example DYNASYLAN(copyright) HS 2907.
The novel process may generally be carried out as follows:
the coating agent, which is generally liquid, may be introduced directly into a bed of powder flame retardant, e.g. ammonium polyphosphate, fluidized by introducing a gas. This usually results in encapsulation of the particles of the flame retardant with the coating agent, during which the coating agent reacts with the surface of the flame retardant and alcohol of hydrolysis and water of condensation, respectively, may be liberated.
After application of the coating agent, the flame retardant treated in this way is, if desired, freed in a subsequent mixing procedure from any water of condensation and, respectively, alcohol of hydrolysis still adhering thereto, e.g. by introducing hot dry air and reducing the pressure. Whereas the coating processes known hitherto operate in an organic solvent, the process of the present invention generally does not require any type of auxiliary material which is complicated to handle or particularly polluting in the environment.
The present process may also include the following process techniques:
(1) Converting the flame retardant to be coated into a fluidized bed in a suitable apparatus, examples of which are mixers of various speeds or the like, so that the powder flame retardant introduced is constantly in motion, with contact between the individual particles uninterrupted. A gas, e.g. or, nitrogen or CO2, may also be fed to the apparatus, the gas being preheated if desired. It is also possible to use an apparatus which can be heated.
(2) Introducing the coating agent in very evenly distributed form into the fluidized material, by injection or dropwise addition or spraying the coating agent into the fluidized material.
The amount of the coating agent to be applied generally depends on the application of the flame retardant and is usually dependent on the magnitude of the specific surface area of the flame retardant, and also on the amount of the flame retardant. For example, the ratio of the specific surface area of the flame retardant to the wetting area per unit of coating agent for a monomolecular layer can be used as a guide.
Using the present invention, surface-modified flame retardants can be obtained in a simple, cost-effective and environmentally friendly manner. Moreover compared with untreated flame retardants or those treated with other coating agents, the flame retardants also have lower water solubility and advantageous properties for further processing in polymer compositions. For example it is possible to add relatively large amounts of the flame retardant (filler level), with easier incorporation, and with less effect on physical properties.
The flame retardants surface-modified and stabilized by the novel process can be incorporated into many combustible polymers with particularly advantageous effect, for example, into polyolefins, such as polyethylene, polypropylene and polystyrene and its copolymers, such as ABS and SAN, saturated or unsaturated polyesters, polyamides, epoxy resins, phenolic resins, furan resins and polyurethanes, and also natural or synthetic rubbers.
Novel surface-modified flame retardants may, however, also be used advantageously for the intumescent coating of combustible materials. The flame retardants according to the invention may also be used to provide flame retardant or flame proof combustible naturally occurring materials, such as wood, particle board and paper, or these may be given an intumescent coating using a dispersion containing the novel flame retardants.
The halogen-free nature of the novel flame retardants is also advantageous and means that the products produced from them fulfill the market""s increasing demand for environmental compatibility. The present invention therefore also provides the use of novel flame retardants in polymer compounds and for rendering combustible naturally occurring materials flame retardant.